The standardization organization 3GPP is studying Long Term Evolution (LTE), which is a communication scheme as a successor to a wideband code division multiple access (WCDMA) scheme, high-speed downlink packet access (HSDPA) scheme, high-speed uplink packet access (HSDPA) scheme or the like (Release-8, 9). Release-8, 9 LTE (hereinafter referred to as “REL8, 9-LTE”) defines an orthogonal frequency division multiplexing access (OFDMA) scheme as a radio access scheme for improving frequency utilization efficiency on a downlink.
Furthermore, REL8, 9-LTE defines a radio transmission method (MIMO: Multiple-Input Multiple-Output) for improving communication quality by providing a transmitter and a receiver with a plurality of antennas respectively (e.g., 3GPP TR 25.913[1]). MIMO transmission improves a transmission rate by transmitting different pieces of information from respective transmitting antennas at the same frequency and at the same timing. Furthermore, REL8, 9-LTE defines a reference signal configuration for channel estimation corresponding to a radio base station apparatus having a maximum of four transmitting antennas.
However, for LTE, a simultaneous channel estimation method for a plurality of radio base station apparatuses remains as a problem yet to be solved. A conventional reference signal configuration does not support MIMO transmission covering a plurality of radio base station apparatuses, and therefore reference signal are not orthogonalized to each other among the radio base station apparatuses. For this reason, when channel estimation is performed among the plurality of radio base station apparatuses simultaneously, there is a problem that the estimation accuracy deteriorates due to interference.